This invention pertains to a particular lining for insulating large diameter lines or pipes carrying high temperature gases and/or fluidized solids for forming a well insulated pipe which is resistant to high temperatures as well as resistant to shock loads and thus has high mechanical strength.
An exemplary pipe is a fluid catalytic cracking unit (FCCU) regenerator flue gas line for carrying gases at temperatures generally in the range of 1,000.degree. to 1,500.degree. F. (538.degree.-816.degree. C.) and pressures in the range of one to four atmospheres, absolute (1.0333-4.133 Kg/cm.sup.2).
Various insulated pipes have been used, but the problems of providing a minimum of expansion in the pipe by having very good internal insulation and having the internal insulation strong enough to withstand stress due to pressure variations and solids flowing at high velocities therein are difficult to solve. Another problem to solve or purpose is to obviate high alloy construction where temperatures exceed those for which allowable stress values are set for carbon steel and low alloy steels, which steels are desired to be used in pipes. Two types of internal insulation for pipes have been used but they fail to withstand flowing conditions and/or stresses encountered in service.
1. Jacketed insulation (batts or block).
Materials having good insulating properties are usually low in mechanical strength. They have been used with a covering of metal sheet to protect them from damage by the high velocity flowing gas stream. These linings have had a relatively short service life. Metal sheeting has generally been eroded, torn, or otherwise damaged, and insulation has been removed by the gas flow. Wrinkling of the metal due to differential expansion, in excess of that allowed for, is though to have been a factor in some of these failures.
2. Castable, or gun-applied, insulation.
These linings may be monolithic applications of a medium weight refractory castable or a two component lining consisting of a layer of a light weight insulating castable protected by a layer of an erosion resistant, high density, refractory castable reinforced with carbon steel or an alloy steel hex metal grating. These have failed repeatedly in areas where lines are subject to vibration, particularly near regenerator flue gas slide valves and orifice chambers. In other cases, a castable insulating lining has been covered with a thin gauge metal jacket. In the latter cases, the metal sheet would apparently expand, vibrate, become wrinkled, flop around, and eventually tear loose, followed by deterioration of the castable insulating lining.